textproduct: Albany

WHAT HAS CHANGED

Confidence has increased in freezing rain potential for Saturday afternoon into Sunday resulting from a complex winter system. Therefore, we have included more ice in the weather forecast especially for areas within the Southwest Adirondacks and Mohawk Valley.

KEY MESSAGES

- Wetted road and walking surfaces from snow melt, brought on my mild temperatures, and widespread rain showers from a passing cold front today, could pose slick travel conditions early Saturday morning as low temperatures fall below, to, and just above freezing tonight and winds decrease.

- Hazardous road conditions with the potential for isolated power outages within portions of the Southwest Adirondacks, Eastern Catskills, Helderbergs, Berkshires, and Southern Greens Saturday afternoon into Sunday afternoon due to light ice accretion from freezing rain and light snow accumulation. - Minor river rises from snow melt and upcoming rainfall will result, at most, in nuisance ponding of water immediately along river banks. The brief duration of above-normal temperatures and expectation for low amounts of precipitation have significantly reduced the potential for ice jams.

DISCUSSION

KEY MESSAGE 1... A low pressure system and potent upper-level shortwave will track to our north through southern Quebec this afternoon through late tonight, forcing a series of fronts to swing through the region. Initially, a warm front will cross through the region from west-northwest to east-southeast with an accompanying batch of showers. While the best forcing will be displaced to our north, the orientation of the incoming upper- level jet associated with the shortwave will place us in its favored right entrance region. This, in tandem with deep southwesterly flow to provide moisture; a surge in warm air advection; and overall lift from the passage of the front itself, will provide more than enough forcing for ascent to make showers fairly widespread in coverage. Additionally, while most showers will be light in nature, some could become locally moderate especially within the Southwest Adirondacks, Mohawk Valley, and Upper-Hudson Valley this afternoon where some elevated instability intersects steepened mid-level lapse rates near 6.5 C/km within the pseudo-warm sector of the system. And, while winds will already be on the breezier side given the steepened pressure gradient and at least partial mixing down of the 60-70kt 850mb jet, rapid cooling and precipitation loading could also lead to some stronger wind gusts within heavier showers this afternoon.

The warm front will clear our region by late this afternoon with showers departing with it to the east and generally tapering off. A second, less widespread batch will then approach just ahead of the incoming cold front, also tracking from west- northwest to east-southeast across the region. These will be light in nature and will likely fall apart before making much eastward progress past the Capital District. However, winds will become increasingly gusty as cold air advection increases in magnitude and expands across eastern New York and western New England.

The passage of the cold front will be completed by late this evening with dry, northwest flow bringing the return to regionwide dry conditions. Winds will gradually decline late this evening into early tomorrow morning while temperatures drop into the mid/upper 20s to low/mid 30s. With mild highs today (values largely in the 40s) leading to snowmelt and showers wetting surfaces further, it is possible that some road and walkways could become slick by early tomorrow morning. This will be especially true for those surfaces that go untreated. Now, there will be limitations to the extent of freezing that happens on wetted surfaces due to the elevated winds for much of the night. But just be aware that patches of untreated, sheltered, and/or elevated roadways could be slick tomorrow morning which would potentially make travel hazardous.

KEY MESSAGE 2... A complex winter storm will impact the region Saturday afternoon through Sunday afternoon, bringing rain; snow/sleet; and freezing rain across eastern New York and western New England.

As an upper-level cyclone deepens over the Upper Midwest Saturday morning, a broad area of low pressure begins to take shape across the western Great Lakes/Ohio Valley regions beneath its far southward- extending trough. Meanwhile, a southern stream trough begins to align with the axis of the aforementioned disturbance in the northern stream such that a surface wave of low pressure near the Mid-Atlantic deepens into a low. By Saturday afternoon, the upper-level cyclone will have deepened further and drifted farther south while its associated area of surface low pressure drifts north and east into the Eastern Great Lakes. Simultaneously, the secondary surface low drifts off or near the Mid-Atlantic coastline, extending a warm front horizontally eastward. Strong surface convergence intersecting strong upper-level jet dynamics and low-level warm air advection will force the development of a broad area of stratiform precipitation that will spread into the region from south to north beginning Saturday afternoon.

The precipitation type forecast remains a bit of a challenge at this time, though confidence is increasing in at least higher terrain regions of the Southwest Adirondacks and Mohawk Valley seeing some freezing rain and/or sleet especially at the onset of precipitation. With our favored position within the right entrance region of the anticyclonically curved upper-level jet, a northerly component of the wind will dam cold air from a nearby high to the north against northward-facing slopes of the Adirondacks such that surface temperatures will remain below freezing while the low-levels warm above. The challenge will be deciphering whether or not the warm nose will be sufficient to make the precipitation at the surface be in the form of freezing rain or sleet. For now, we have erred on the side of freezing rain given the sufficient warm nose shown on forecast soundings. However, this may not be the only place to receive some ice. With a high located in the western Atlantic and prevailing surface flow out of the southeast, some cold air could also be dammed against southeast-facing slopes of the Eastern Catskills, Helderbergs, Berkshires, and Southern Greens. Forecast soundings allude to this as well, though sources of guidance are a bit more varied in whether or not surface temperatures will remain below or above freezing. All other areas will be warm enough to see primarily rain with a slight chance of a rain/snow mix at onset.

On the back side of the system, cold air advection will erode the warm nose and allow precipitation, which will become confined to higher terrain areas where upslope flow will play a major role in maintaining it, to transition back to snow. When all is said and done, ice accumulations look to range from 0.01" to roughly 0.15" across our high elevation areas with the highest accretions within the Southwest Adirondacks. Snow will primarily also be confined to higher terrain areas with totals ranging from a couple tenths to around 2" in the Southwest Adirondacks. Total liquid precipitation across the region looks to range from about 0.25" to 0.5".

The combination of light snow and ice accumulations will make for slippery travel conditions Saturday night and Sunday especially in the Southwest Adirondacks. Additionally, isolated power outages will be possible due to ice accretion that could weigh or knock down power lines and tree limbs. Caution is advised for anyone who may be out and about Saturday late afternoon through Sunday afternoon.

KEY MESSAGE 3... While we remain in an above-normal temperature pattern for much of the next week, temperatures will not become warm enough to pose major break-ups of river ice. Additionally, despite the rainfall and snowmelt that we are anticipated to have through the weekend, river forecasts only show an approach to Action Stage at most. Therefore, ice jam flooding and any flooding in general is not anticipated and remains a non-concern.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Through daybreak, mixed conditions at the TAF sites, with some areas of fog/low stratus already developing at KGFL and KPSF. Expect occasional IFR/LIFR conditions at these sites through sunrise, though a few brief periods of VLIFR will be possible as well. At KALB, a few brief periods of IFR/LIFR will be possible until 08Z/Fri, then mainly VFR as south winds increase. KPOU should remain VFR although brief fog/low stratus possibly developing prior to 08Z/Fri.

After daybreak, VFR Vsbys and VFR/MVFR Cigs are expected with occasional stratus developing, trending to MVFR (for Cigs) this afternoon. An approaching cold front will bring some rain showers to the TAF sites after 18Z/Fri, with brief periods of MVFR Vsbys also possible through early this evening, and at KPOU, brief ground fog could develop and reduce conditions to IFR/LIFR. Overall conditions should slowly lift to VFR toward and after 06Z/Sat in the wake of the cold front.

Light/variable winds through daybreak except becoming south/southeast at 5-10 KT at KALB. After daybreak, south winds will increase to 8-15 KT by mid/late morning with some gusts of 25-30 KT possible, especially at KALB and KPSF where some gusts up to 35 KT can not be ruled out. Winds will then shift into the west between 03Z-05Z/Sat as the cold front crosses the region. Low level wind shear will occur after sunrise and continue much of Friday as strong south winds around 2000 FT AGL develop, reaching 40-50 KT while surface winds remain generally 10-20 KT with some stronger gusts (mainly at KALB/KPSF).

Outlook...

Saturday Night: High Operational Impact. Definite RA...SN. Sunday: Moderate Operational Impact. Chance of RA. Sunday Night: Low Operational Impact. Breezy. Slight Chance of SHSN. Monday: Low Operational Impact. Breezy. NO SIG WX. Monday Night: No Operational Impact. NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: Low Operational Impact. Slight Chance of SHRA. Wednesday: Moderate Operational Impact. Chance of SHRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.